Tuesday, January 25, 2011

Kiteboard Design - Broad Parameters.

Overview

Kiteboard design remains a bit of a black art even though there is a lot of feed in from surfboard, windsurfer and boat design. There appear to be some accepted wisdoms about what does what on a board but it seems that in reality the different parameters have a highly non-linear relationship and board performance is dependant on the relative amounts of each so that ultimately design needs to be honed through prototyping and testing.

A blog/website by Derek Comancho http://www.dcboardz.com/kite.html sums it up nicely

"Kiteboard designing is not a defined equation, it is a combination of all the things I have mentioned above and more. It all has to work together in synergy. There is a lot of high tech 'know how' in terms of the materials used and construction technique used, but just like surfboard making, there is still a big part of personal feel by the shaper that has to go into the shaping and making of a great kiteboard . The shaper is still a big part of the process to get the 'great feel' of a custom board that has not been able to be reproduced by machines in a factory. This is where knowledge, creativity and skill meet to make art"

So what does this mean for the virgin kiteboard project? It means I'm going to get out my tape measure and start by copying the bejezez out of my favourite board ( also my only board) and tweaking it for what I think might improve its performance in our local conditions.

The terms

Here is good intro to the meanings of some of the key design terms and the authors view on how they affect the boards performance.

http://www.session1.com/all-kite-surf/buyers-guide/kiteboards-c-624_124_253_483.html

A website of Derek Comancho mentioned above has some really information about the relationship between pairs of features and the usual stuff - rocker, flex width/length with some interesting explanations involving the flow and release of water. http://www.dcboardz.com/kite.html


My design goals

I'm keeping the design goals of the board pretty humble given it the first one. Once it completed I'll start tweaking the parameters of the board and reference those back to this first board to see whether any insights emerge.

The board is going to be used mainly for freestyle riding but in the pretty choppy conditions we get locally.

My current board is a crazyfly raptor 132x41cm full carbon board. It has a progressive rocker meaning its relatively flat through the middle and the rocker kickers up at the ends. There is only about 2.5cm of rocker in it at each tip and about 5 mm single concave.

Things I like about it

  • big planing area so its good in lighter winds


  • Its very stiff and so when you can hold the edge down it pops really well

  • Despite having 50mm fins its tracking is skatey enough to not grab to hard when you're coming in fast after unhooking.


  • Wide stance - you can beat it for feeling stable


  • Tips are not too square so the board carves nicely in the waves without having to bear down too hard to get the rear toeside tip to get traction.


Things I'm not so fussed about with it


  • 41cm is a wide board for my weight. I find it quite remarkable what a difference there is between 40cm and 41 cm. As the wind picks up the 41cm wide board looses it edge a long time before the 4ocm. I guess this makes sense because if you think about the forces acting on the edge of the rail you have the force of the water trying to make your board rotate about your heal and lay flat. The distance from your heal to the edge of the board is typically just a few centimeters and so a 1cm in the width can corresponds to as much as 33% increase in the torque trying to rotate the board about your heal. With this in mind it make sense that a centimeter or so is a material amount when it comes to width.


  • The rocker profile does not deal with chop well. The progressive increase in the amount of rocker at the tips means the leading tip underside slams into the chop and goes straight into you knees and also throws up a lot of spray. This means that you need to lean back hard on you back foot to get the nose up which leads to aching legs in no time. The continous rocker boards with slightly more rocker are far superior in the chop.
    So the broad parameters for this board will be:
    i) 129x 39cm with the outline similar to the raptor pro except that the tips will be a bit more squared off. (For a really square board have a look at a slingshot lunacy and try to ride it in the surf).
    ii) continuous rocker with 3.5cm at each tip to help with handling the chop
    iii) 10mm concave together with small fins. My hope is that this will maintain the upwind ability (concave) but allow the board to skate a big more when coming in hot (the small fins)
    iv) Stiff through the mid section and increase the flex in the tips again to help smooth the way through chop a bit.
    v) 10mm abs plastic rails because that's what I had on hand. However, in the next board I'd like to try wrapped rails (reinforced with carbon) so that I can experiment with the rail shapes.
    vi) wide stance 18" instep to instep.
    vii) lots of 'duck' in the footpad angles because I'm part Chinese and walk like I have flippers on
      vii) No grab handle because it forces you to carry it like a hand bag and that's just not ok:)

    1 comment :